X-ray evidence of increased asbestos exposure in the US population from NHANES I and NHANES II, 1973-1978. National Health Examination Survey

Our plain-English summary of X-ray evidence of increased asbestos exposure in the US population from NHANES I and NHANES II, 1973-1978. National Health Examination Survey, by W.J. Rogan, N.B. Ragan, G.E. Dinse (Cancer Causes & Control, 2000).

The study

• Authors: W.J. Rogan, N.B. Ragan, G.E. Dinse
• Journal: Cancer Causes & Control
• Published: 2000;11(5):441-9
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: Jobs involving heavy asbestos exposure increase risk for lung cancer and mesothelioma substantially, and low-level exposures may carry some risk. At least one indicator of asbestos exposure, mesothelioma, has been increasing in the US for decades. We investigated the prevalence of another indicator, pleural thickening on x-ray, in a defined sample of the US population.

Methods: Certified physicians read 1060 x-rays from the second National Health and Nutrition Examination Survey (1976-1980) for pleural changes consistent with pneumoconiosis, which are a reasonably specific indicator of asbestos exposure.

Results: Prevalence estimates, in NHANES II, in the age group 35-74 years, are 6.4% (+/- 0.9%) among males, 1.7% (+/- 0.6%) among females, and 3.9% (+/- 0.6%) overall. These prevalences are approximately twice those estimated from NHANES I data (1971-1975).

Conclusions: X-ray evidence of asbestos exposure was common in the late 1970s and increasing. The increase may be due to occupational asbestos exposure, but it is so large as to suggest some contribution from environmental, non-occupational asbestos exposure.

In plain English

This study estimated how common dust-related pleural thickening, a chest x-ray change the authors used as a marker of past asbestos exposure, was in the US population in the late 1970s. Three certified "B" readers re-read sampled chest x-rays from the second National Health and Nutrition Examination Survey (NHANES II, 1976 to 1980). Of these, 1060 were readable, and 115 were called positive by at least two readers. For people aged 35 to 74, the estimated prevalence was 6.4% in males, 1.7% in females and 3.9% overall. The authors' earlier NHANES I estimates for the same ages were 3.2%, 0.2% and 1.6%. Male prevalence doubled, while female and overall prevalence rose by more. A single reader re-read x-rays of white males aged 45 to 74 from both surveys. This reader found a rise from 7.2% to 13.0%, which the authors called a relative increase nearly identical to the three-reader result. The authors acknowledged that not all pleural thickening seen on x-ray is caused by asbestos, and that only one reader took part in both surveys. They concluded that x-ray evidence of asbestos exposure was common and increasing, and that the increase was large enough to suggest some contribution from environmental, non-occupational exposure.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cross-sectional prevalence study: a stratified sample of national survey chest x-rays was re-read, and the results were compared with the authors' earlier estimate from the previous survey made with the same methods
• Who was studied: Chest x-rays from NHANES II (1976 to 1980). NHANES II was a cluster sample of about 28,000 non-institutionalized, non-military US residents, of whom 8213 were aged 35 to 74. Of 1207 x-rays selected for re-reading, 1060 were located and readable. These were compared with the earlier NHANES I (1971 to 1975) results.
• Exposure: Individual asbestos exposure was not measured, and no fiber types were named. Dust-related pleural thickening on chest x-ray served as an indicator of past asbestos exposure. Three certified B readers read the x-rays using the 1980 ILO protocol, and an x-ray counted as positive if two or more readers called it positive.
• Main results:
  • Of the 1060 readable NHANES II x-rays, 115 were classed as positive and 945 as negative.
  • Estimated NHANES II prevalence in people aged 35 to 74 (standard errors in parentheses): 6.4% (0.9%) in males, 1.7% (0.6%) in females, 3.9% (0.6%) overall.
  • The corresponding NHANES I estimates for ages 35 to 74 were 3.2% (0.7%) in males, 0.2% (0.1%) in females and 1.6% (0.4%) overall. The authors described the NHANES II estimates as approximately double these. That holds for males, but female and overall prevalence rose by larger factors.
  • For ages 25 to 74, assuming no cases at ages 25 to 34, NHANES II estimates were 4.5% (0.6%) in males, 1.2% (0.5%) in females and 2.8% (0.4%) overall. The corresponding NHANES I estimates were 2.3% (0.6%), 0.2% (0.1%) and 1.2% (0.3%).
  • A single reader re-read x-rays of white males aged 45 to 74 from both surveys. The estimated prevalence rose from 7.2% (1.3%) in NHANES I to 13.0% (1.7%) in NHANES II. The authors described this as nearly identical to the relative increase in the three-reader estimates for that group, which went from 3.7% to 7.1%.
  • The single reader's first and second readings agreed 91% of the time. The kappa index (agreement beyond chance) was 69% (2%).
  • The authors then shifted age groups by 5 years to follow the same birth cohorts. After this shift, prevalence in every age group in 1978 was larger than in the previous 5-year age group in 1973.
  • Only some of these cohort-adjusted increases were statistically significant.
  • The highest subgroup prevalences were among nonwhite males and females in certain age groups, for example 28.6% in nonwhite males aged 55 to 59. The authors described these estimates as unstable because they rest on very few x-rays.
• The authors' conclusion: The authors concluded that x-ray evidence of asbestos exposure was common in the late 1970s and increasing. They wrote that the increase may be due to occupational exposure, but is large enough to suggest some contribution from environmental, non-occupational asbestos exposure.
• Limitations the authors state:
  • Not all pleural thickening seen on x-ray is caused by asbestos; some turns out to be fat or other material.
  • Different readers were used in the two surveys, with only one reader in common, so differences in reader sensitivity could affect the comparison. The authors checked this with a single-reader re-reading.
  • The single reader's agreement with their own earlier readings was only moderate.
  • Some other exposure could produce pleural thickening resembling that from asbestos. The authors considered smoking and obesity and argued against them as explanations for the increase.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Lung cancer, Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Lung Cancer, Mesothelioma, Pleural Thickening, Pneumoconiosis.

Related studies

• US prevalence of occupational pleural thickening. A look at chest X-rays from the first National Health and Nutrition Examination Survey — W.J. Rogan, B.C. Gladen, et al. (1987)
• Relationship of mortality, occupation, and pulmonary diffusing capacity to pleural thickening in the First National Health and Nutrition Examination Survey — D.P. Loomis, G.W. Collman, et al. (1989)
• Re: "US prevalence of occupational pleural thickening: a look at chest x-rays from the first National Health and Nutrition Examination Survey" — W.C. Cooper (1989)
• The National Sheet Metal Worker Asbestos Disease Screening Program: radiologic findings. National Sheet Metal Examination Group — L.S. Welch, D. Michaels, et al. (1994)
• Cancer Risks among Welders and Occasional Welders in a National Population-Based Cohort Study: Canadian Census Health and Environmental Cohort — J.S. MacLeod, M.A. Harris, et al. (2017)
• Development of a medical examination program for former workers at a Department of Energy national laboratory — P.N. Breysse, V. Weaver, et al. (2002)

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